1. Field of the Invention
The present invention relates to a solid pole oxygen sensor and its manufacturing process.
The oxygen sensor is a means of measuring the equilibrium oxygen partial pressure in, say, the exhaust gas from an automotive engine.
2. Description of the Prior Art
Prior art oxygen sensors have a solid electrolyte vessel made of a solid electrolyte such as zirconia stabilized by yttrium oxide, etc. On the outside and inside surfaces of this vessel are formed internal and external electrode layers of platinum or platinum alloy film. The vessel is filled with an internal reference substance, i.e., a gas with a constant oxygen content like air or a solid with a constant equilibrium oxygen partial pressure such as a mixed powder of metal-metal oxide.
The ratio between the equilibrium oxygen partial pressures of a gas to be measured, which comes into contact with the external electrode layer and the internal reference substance which is in contact with the internal electrode layer is converted to an electromotive force, by which the equilibrium oxygen partial pressure in the gas to be measured can be determined. As the internal reference substance in said oxygen sensor, a gas or a solid is available. Functionally and structurally, the solid has been found to be better than the gas, when it is to serve as part of automotive equipment.
However, the conventional solid pole oxygen sensor, including a solid electrolyte vessel, which involves a difficult step of calcining of the vessel or high-temperature firing for manufacture, is complicated in structure and unfit for miniaturization. Moreover, it is difficult to take out of the vessel the potential of the internal electrode layer in the solid electrolyte vessel.